Design And Experimental Study Of Straw Facultative Pretreatment Device

Our country is an agricultural country,every year the production of crops straw resources are abundant.The unreasonable utilization of straw resources brings a lot of environmental pollution and waste of resources.However,due to the structure of the straw,anaerobic digestion started slowly,and the yield was low.Therefore,it is necessary to pretreatment the straw to break its internal structure and raise the rate of anaerobic fermentation.Biological pretreatment can effectively destroy the internal structure of straw,the degradation of wood fiber,the use of bio composite bacteria pretreatment research has also been attracted great attention recently.At present,a lot of research on the pretreatment technology of bio composite bacteria is carried out,but the research on the related equipment is not mature.The design of pretreatment device,the monitor of process parameters of pretreatment,the transfer of pretreated materiel and matching with anaerobic fermentation to realize continuous production,utilization of the biological heat in the process of pretreatment and other issues need to be further studied.Based on the above problems,the straw pretreatment device was designed.The device is composed of a cylinder,a double helix spiral belt stirring device,a temperature monitoring system,a ventilation system and a heating system.Under the combined action of aerobic and micro aerobic microorganisms,the macromolecular substance such as lignin,hemicellulose and cellulose,was converted into small molecules and water soluble substances rapidly.The water soluble substance can enter the material liquid storage tank with the leachate,then according to the amount of process to enter the anaerobic fermentation device.The auger of the pretreatment device can realize the mixing of the material under the normal station.Under the feeding station,the solid material can be transferred to the following anaerobic fermentation device through auger device.The conveying process not only realizes the transportation of reactive materials,but also transfer the biological heat to anaerobic fermentation device,supplying heat for anaerobic fermentation equipment.In order to verify the pretreatment effection of the straw pretreatment device,the preliminary experimental study on the compound bacteria pretreatment of con stalkwas carried out.The results showed that the hemicellulose degradation rate of the pretreated straw was 33.22%,the degradation rate of hemicellulose was 21.94%,and the lignin degradation rate was 30.63%.After scanning electron microscope analysis of the pretreated corn straw,the straw was obviously degraded,and a large number of cracks and holes were found on the surface of the micro structure.But the effect of decomposition is slightly lower than that of the 30 L small pretreatment device.In the engineering application,it is necessary to adjust the operating parameters to test and study,so that the heat treatment and the straw decomposition effect can reach the best condition.Then the experimental study on the effect of ventilation rate on the compound bacteria pretreatment of corn straw was carried out.The experimental results show that,in the case of fixed ventilation,ventilation volume is too large or too small will cause adverse effects on the decomposition of straw.Ventilation volume is too large will make moisture and heat loss too fast.Ventilation is too small can not meet the demand for good oxygen content,and cause microbial decomposition of the material is not sufficient.In the different stages of the reaction,adjusting ventilation according the change of oxygen content in tail gas outlet,it can make the microbial get sufficient oxygen,accelerates the decomposition of the organic matter in the straw,and ensure temperature and moisture will not lost too fast.Under this ventilation scheme,the temperature of material can up to the maximum.It is beneficial to the subsequent anaerobic fermentation using the heat produced by it.,and the decomposition effect after pretreatment of straw is the best,the pretreated straw can be used as high quality raw materials of anaerobic fermentation.According to the test results,the characteristics of heat production in the pretreatment process were analyzed.By using the curve of temperature and time in the pretreatment process,the polynomial of temperature time is fitted.Then according to the principle of energy conservation,the mathematical relation of temperature field is established,and the heat conduction differential equation is obtained.Derived from the formula,the measured physical parameters are introduced to obtain the heat experience formula of the internal heat source.In order to further verify the accuracy of empirical formula,useing FLUENT software to simulate the temperature field,the simulation results agree well with experimental results.It is proved that the mathematical model established above is accurate and has reference value for the later experiment.The Fluent model can be used to predict and analyze the temperature field distribution in the process of the pretreatment process,adjust and optimize theparameters of the mixing device,the discharging device,the ventilation volume and so on.